This invention relates to a method of extracting protein from vegetable seeds. With more and more vegetable protein going into human food, efficient extraction from vegetable seed flakes assumes more and more importance. Commercial extraction yields 30 percent or less of the weight of soybean flakes, and ideal laboratory extraction yields 42 percent of defatted flakes (A. K. Smith, In "Processed Plant Protein Foodstuffs," Ed. A. M. Altschul, Chapter 10, Academic Press, New York, 1958). For maximum yield of proteins, the flakes are unheated; but for maximum nutritive and flavor quality, the flakes require a moist heat treatment (i.e., toasting) (S. J. Circle and A. K. Smith, Ed., In "Soybeans: Chemistry and Technology," Chapter 9, Avi Publishing Company, Inc., Connecticut, 1972). Toasting causes protein denaturation which means low yields, diminished functionalities, and limited applications.
Up to now, extraction of vegetable proteins has been mostly done by conventional-stir (Circle and Smith, supra). Results from that method are good on untoasted flakes but poor on toasted flakes. High-speed stirring has been reported to grind the sample during extraction [T. M. Paulsen et al., J. Amer. Oil Chem. Soc. 37: 165 (1960)]. Other factors affecting protein solubility have been reviewed (S. J. Circle, In "Soybeans and Soybean Products," Ed. K. S. Markley, John Wiley and Sons, New York, 1950; and W. J. Wolf, In "Soybeans: Chemistry and Technology," Ed. A. K. Smith and S. J. Circle, Chapter 4, Avi Publishing Company, Inc., Connecticut, 1972).
Although sonication has been applied in the past to disintegrate and solubilize animal and plant tissue components (I. E. El'Piner, In "Ultrasound: Physical, Chemical and Biological Effects," Chapter VII, Consultants Bureau, New York, 1964; and D. Ensminger, In "Ultrasonics, the Low- and High- Intensity Applications," Marcel Dekker, Inc., New York, 1973), a search of literature indicates that it has not been applied to improve the extraction of proteins in vegetable seed flakes.
In accordance with the invention, I have discovered a method of extracting protein in high yields from vegetable seeds comprising sonicating a vegetable seed composition selected from the group consisting of full-fat vegetable seed flakes, meal, grits, and flour and their defatted analogs and their cooked full-fat and defatted analogs in a suitable solvent. This is accomplished in a solids:solvent ratio of from about 1:10 to 1:40, at a sonic frequency of about 20 KHz and at a sonic output power of from 100 to 500 watts for a time sufficient to solubilize from about 50 to 100 percent of the total protein in the vegetable seed composition. The solids and supernatant solution of proteins are separated using ordinary means, and the protein fraction is then recovered from the solution.